In a typical fuel cell system, hydrogen or a hydrogen-rich gas is supplied through a flowpath to the anode side of a fuel cell while oxygen (typically in the form of air) is supplied through a separate flowpath to the cathode side of the fuel cell. In one form of a fuel cell, called the proton exchange membrane (PEM) fuel cell, an electrolyte in the form of a proton-transmissive membrane is sandwiched between the anode and cathode to produce a layered structure commonly referred to as a membrane electrode assembly (MEA). Each MEA forms a single fuel cell, and many such single cells can be combined to form a fuel cell stack.
Water results from and is required for the operation of a fuel cell system, including a PEM-based system. Protons (derived from fuel present in the anode flowpath) are conducted from the anode through the PEM to the cathode, wherein such protons react with oxygen present in the cathode flowpath to produce water which is directed away from the anode and cathode. However, during operation of a fuel cell, water can build up in the anode flowpath. This may be due to, among other things, the diffusion of water from the fuel cell's cathode to the anode. If the amount of water present at the anode becomes too great, the anode can flood, causing damage to the fuel cell. Other forces, however, can cause the anode flowpath to completely dry out, which is also damaging because at least some water needs to be present in the fuel cell in order to maintain hydration of the PEM. Because water is omnipresent in an operable fuel cell system, problems can arise in cold temperature situations as prolonged exposure to such conditions may cause the water in the system to freeze. Ice in the fuel cell system, and in particular within the anode flowpath, can prevent proper performance of the system and may also damage the system.
Under freeze start conditions (typically when the internal fuel cell temperature has been at from 0° C. to −20° C. for a prolonged period of time), a fuel cell can be, or become, blocked with ice. If the anode or anode flowpath is blocked, the cell goes to negative voltages after consuming all of the hydrogen within the cell. Even after the load is removed, it takes a substantial period of time to get back to the open circuit voltage (OCV). Thus, the design of a fuel cell requires that attention be paid to the amount of hydration to ensure that neither too much nor too little water is present, and that the water that is present is managed in a manner that allows for proper performance of the fuel cell, particularly under freeze start conditions.
Water separators are one way to manage the amount of water present in an anode or anode flowpath. Current water separation technologies are configured to operate in unidirectional or bidirectional flow directions. However, such water separators comprise valves and other components, as well as design configurations, that can impact the successful start up of a fuel cell system. For example, while anode inlet valves of conventional water separators are fairly reliable, they can nevertheless become blocked with ice. In part, this can be due to the temperature of the valve remaining at freezing temperatures upon and after initial operation of a fuel cell system under freezing conditions. Therefore, there is an ongoing need for fuel cell system components that ensure reliable start-up and water management, particularly under freeze start conditions.